[djsumdog]

You mean Google is discontinuing the API? (They had an API? They removed XMPP federation and eventually support, if that's what you mean).

The libpurple/Hangups projects for chat clients is the work of reverse engineering the existing Hangouts protocol (which apparently heavily relies on protocol buffers).

[detaro]

Yes, they had an API which could control and customize Hangouts https://developers.google.com/+/hangouts/